1. Field of the Invention
The present invention relates to an improved method for converting .beta.-keto esters to ketones, and to novel ketones produced therefrom. Specifically, this invention relates to the method of decarbalkoxylating alkylated .beta.-keto esters using a phase-transfer agent to yield ketones. The present invention also relates to novel methylene-linked pyrethroid insecticides produced by the method of the invention.
2. Description of the Prior Art
Ketones are very valuable commercial compounds. One synthetic route for the preparation of ketones is via the conversion of alkylated .beta.-keto esters. Classical synthetic approaches to such conversions are known. For example, it is known that acid-catalyzed decarboxylation in an aqueous or nonaqueous medium, following alkaline hydrolysis of .beta.-keto esters provides simple access to ketones. However, because this conversion method can be unpredictable, with little or no yield, its use as a commercial synthetic process is not desirable.
Several previous and more recent approaches to ketone synthesis through conversion of .beta.-keto esters employ a retro Claisen-type reaction. Such syntheses require a nonaqueous medium and/or high reaction temperatures, thereby presenting a potential environmental hazard and necessitating much time and expense. Also, the retro Claisen-type reactions are undesirable since they may require another method to complete the synthesis. For example, when a crown ester is used to convert several .beta.-sp.sup.2 carbon ester compounds to carboxylates in an alkaline medium, acidification and/or thermolysis are required to complete ketone synthesis.
Consequently, there exists a need for a method of converting alkylated .beta.-keto esters to ketones which is more predictable, cost effective, and environmentally safer than prior art processes. In addition, there is a need for a facile approach to the conversion of .beta.-keto esters to ketones which produces a yield which is practical for commercial application.